This description relates to perimeter detection. Perimeter detection systems are useful in detecting intruders along large perimeters, such as those at airports or military encampments. Airports have authorized entrances that are gate-controlled 24 hours a day, but the airports may be surrounded by undeveloped and unmonitored terrain whose perimeters can be several miles. While many airports use full perimeter chain link fencing, this is not always effective. Many currently available perimeter detection systems are detectable by the intruder and are bulky, and may not be easily deployed or hidden. For example, the intruder can detect the perimeter detection system using methods including visual inspection, radio frequency probe, metal detection, and thermal scanning.
In one example, a perimeter detection system uses a sensing fiber whose optical property varies when stress is induced in the fiber, resulting in a change in the optical signals propagating through the fiber. The sensing fiber is deployed along the perimeter of an area to be monitored. A light source generates an optical signal, which travels the length of the sensing fiber, and is detected by an optical detector. A monitoring station monitors the optical signal detected by the optical detector, and detects changes in the detected signal to determine whether stress is induced in the sensing fiber, indicating that an intruder has stepped on the sensing fiber.